Various methods and compositions for targeted cleavage of genomic DNA have been described. Such targeted cleavage events can be used, for example, to induce targeted mutagenesis, induce targeted deletions of cellular DNA sequences, and facilitate targeted recombination at a predetermined chromosomal locus. See, for example, United States Patent Publications 20030232410; 20050208489; 20050026157; 20050064474; 20060188987; and International Patent Publication WO 07/014,275, the disclosures of which are incorporated by reference in their entireties for all purposes.
CCR5, a 7-transmembrane chemokine receptor, is the major co-receptor for HIV-1 entry into CD4 T cells (Samson et al. (1996) Nature 382:722-725; Deng et al. (1996) Nature 381:661-666; Alkhatib (1996) Science 272:1955-1958). Since the discovery of the HIV-1 resistance conferring homozygous Δ32 deletion in the CCR5 gene, CCR5 has been intensively studied as a prime target for HIV therapy. Although small molecules have been shown to induce receptor internalization or block CCR5-HIV interaction (Fatkenheuer et. al. (2005) Nat. Med. 11:1170-1172), these small molecule approaches have resulted in the development of resistance via selection for escape mutants which interestingly continue to use CCR5 for viral entry (Kuhmann et al. (2004) J. Virol. 78:2790-2807). Similarly, intrabody, antisense and RNAi-based approaches have to date only partially blocked CCR5 expression.
Thus, there remains a need for compositions that completely knock-out CCR5 for phenotypic penetrance and long-term resistance to HIV infection.